1. Field of the Invention
The invention relates to non-aqueous inks for ball point pens.
2. Discussion of the Background
Non-aqueous ball point pen inks contain soluble dyes, resins, solvents, additives and other processing aids and are used to fill ball point pen cartridges.
In particular, the ink, which is generally highly viscous, is not supposed to fail at low and high temperatures. By maintaining a certain flow capacity in the ball point pen cartridge, the ability to start writing immediately and continuous writing must be assured even at low ambient temperatures. On the other hand, even at tropical temperatures, running and spotting should not occur. Furthermore, no droplet formation at the ball point pen tip should occur due to the effect of moisture, even in the form of high humidity.
Ball point pen inks, containing soluble dyes, synthetic resins, solvents, and oleic acid, respectively are known (Seifen-Ole-Fette-Wachse 109, 16/1983, pages 481 to 483).
Attempts have been made to improve the control of viscosity, the ability to start writing and the friction wear resistance by using a synthetic resin and polyvinyl pyrrolidone, dissolved in benzyl alcohol or higher glycols, as a thickener (Seifen-Ole-Fette-Wachse 103, 3/1977, page 76). By adding a resin, the viscosity of the ink at room temperature can be adjusted to the desired value. Usually, values in the vicinity of 10,000 to 20,000 mPa.s are found. In this connection, resins which contain hydroxyl groups yield the highest values, with the same throughput amount. As in the case of hydrogenated ketone resins and styrene/allyl alcohol copolymers, they also demonstrate the relatively flattest viscosity/temperature curve. Other binders, such as oil-free alkyd resins, ketone or aldehyde resins, change the viscosity very greatly when the temperature changes, or they are unstable in a ink, such as a novolak, and result in a decrease in viscosity after only a short time.
In general, all of the previously known binders and resins are insufficient as a sole viscosity regulator. Furthermore, an overly high proportion of resin in the ink formulation is undesirable for reasons of production ease and handling of the ink, adjustment of the color intensity and permanence, and partly for price reasons. Polyvinyl pyrrolidone, which is described in the literature, is used as a thickener to increase viscosity. At proportions of about 3% by weight of the total ink, a clear increase in viscosity can be achieved.
However, the problems associated with temperature changes have not been eliminated. Particularly at higher temperatures, such as those which occur in the summer or in the tropics, a large decrease in viscosity of the inks is not prevented or reduced. Another problem is the great sensitivity to moisture of any kind. Thus, slight amounts of water, such as those which can be contained in other ink raw materials, drastically reduce the ink viscosity. If ball point pens are exposed to high humidity, droplet formation occurs in the tip region, or in the case of open cartridges, the ink leaks out.